The operation of gas turbine engines, whether used on the ground for power generation or in flight for propulsion or secondary power, is controlled by an electronic control unit commonly referred to as an ECU. Incorporated in the ECU are control schedules and control logic for the engine. For example, LaCroix, U.S. Pat. No. 4,337,615 discloses a start control logic that is embodied in the engine's ECU. This start control logic, like other control logic in the ECU, is related to fuel flow to the engine and includes calculating the temperature rise in the combustor of the engine. To determine this temperature rise, the ECU must know the heating value of the fuel with the fuel's lower heating value commonly used. Thus, these types of engine controls are developed on the assumption that the lower heating value of the fuel is known and will remain constant during the life of the engine.
Some gas turbine engines are used as pollution control devices. Such devices are disclosed in Dodge et al, U.S. Pat. No. 5,592,811 and Maese et al, U.S. Pat. No. 5,673,553 in which volatile organic compounds, (VOCs), are burned and destroyed in the combustor. A problem that has arisen with the use of gas turbine engines in this manner, is that the in these applications the constituents of the gas or fuel being burned in the combustor can vary greatly resulting in a large variation in the lower heating value of the fuel. Sometimes the heating values can vary as much as fifty percent. It has been observed that large variations in lower heating value change the performance of the engine and can cause the engine to over speed or under speed at its normal operating condition.
Accordingly, there is a need for an engine control system and method that adjusts for changes in the lower heating value of the fuel.